Vehicle engines may be configured to shut-off during idle conditions when the vehicle comes to a stop while a brake is applied and restarted once the brake is released (e.g., a stop/start system) in order to reduce fuel consumption. Fuel consumption may be further reduced by shutting down the engine during braking or by shutting down the engine when the operator is not braking and not requesting torque, before the vehicle has come to a stop.
One approach to shutdown and subsequently restart the engine while the vehicle is traveling is disclosed in U.S. Pat. No. 6,951,525. In the cited reference, the engine is restarted prior to a transition from free-wheel mode to engaged clutch travel mode by employing the fuel injection system using a charge regulator and/or an electric motor. In one embodiment the charge regulator reactivates the engine by sequentially activating a fuel injection system. In an alternative embodiment, engine restart may be supported by an electric motor. However, sequentially activating a fuel injection system to restart an engine is of little use in starting an engine that is not rotating because the injected charge may not be compressed so that it can be combusted and thereby restart the engine. And, starting an engine using a starter can interrupt other electrical systems since a large current may be required to restart the engine.
The inventors herein have recognized the above problems and have devised an approach to at least partially address them. Thus, a method for controlling an engine coupled to a transmission in a vehicle is disclosed. The method comprises, under selected conditions, shutting-off the engine and spinning-down the engine to rest while the vehicle is traveling, and, in response to an operating condition, restarting the engine by at least partially engaging the transmission to assist in spinning-up of the engine from rest while the vehicle is traveling.
Specifically, in one example embodiment when the vehicle is moving, a torque converter or another clutch is engaged when an engine restart is requested. Engaging the clutch transfers wheel torque to the at-rest engine so that the engine is rotated. An electric pump may be driven while the engine is at rest so that hydraulic pressure in the transmission is maintained during engine rest conditions. The transmission clutches can be shifted based on vehicle speed so that a desired amount of starting torque can be applied to start the engine (e.g., top gear reduces the resulting vehicle deceleration rate during a “push start”). In this manner, vehicle inertia can be used to assist in spinning-up the engine from rest when the vehicle is moving. Thus, fuel can be conserved by stopping the engine while engine torque is not required. And, the engine can be quickly restarted without having to engage the starter and draw current from the vehicle battery.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.